EP1023935A1 - Process for selective catalytic reduction of nitrogen oxides in oxygen-containing exhaust gases - Google Patents
Process for selective catalytic reduction of nitrogen oxides in oxygen-containing exhaust gases Download PDFInfo
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- EP1023935A1 EP1023935A1 EP00101564A EP00101564A EP1023935A1 EP 1023935 A1 EP1023935 A1 EP 1023935A1 EP 00101564 A EP00101564 A EP 00101564A EP 00101564 A EP00101564 A EP 00101564A EP 1023935 A1 EP1023935 A1 EP 1023935A1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
- F01N3/2073—Selective catalytic reduction [SCR] with means for generating a reducing substance from the exhaust gases
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/32—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by electrical effects other than those provided for in group B01D61/00
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9413—Processes characterised by a specific catalyst
- B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9431—Processes characterised by a specific device
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2251/00—Reactants
- B01D2251/20—Reductants
- B01D2251/206—Ammonium compounds
- B01D2251/2062—Ammonia
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/10—Noble metals or compounds thereof
- B01D2255/102—Platinum group metals
- B01D2255/1021—Platinum
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/10—Noble metals or compounds thereof
- B01D2255/102—Platinum group metals
- B01D2255/1023—Palladium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/10—Noble metals or compounds thereof
- B01D2255/102—Platinum group metals
- B01D2255/1025—Rhodium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/10—Noble metals or compounds thereof
- B01D2255/102—Platinum group metals
- B01D2255/1028—Iridium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/204—Alkaline earth metals
- B01D2255/2042—Barium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/206—Rare earth metals
- B01D2255/2065—Cerium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/207—Transition metals
- B01D2255/20738—Iron
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/207—Transition metals
- B01D2255/20761—Copper
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/50—Zeolites
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
- F01N2240/25—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being an ammonia generator
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
- F01N2240/28—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being a plasma reactor
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
- Y02C20/00—Capture or disposal of greenhouse gases
- Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S423/00—Chemistry of inorganic compounds
- Y10S423/09—Reaction techniques
- Y10S423/10—Plasma energized
Definitions
- the invention relates to a method for selective catalytic Reduction in lean exhaust gas from internal combustion engines contained nitrogen oxides by reducing the Nitrogen oxides using ammonia on a catalyst.
- the internal combustion engines with lean exhaust gas are diesel engines and lean petrol engines, so-called lean-burn engines.
- diesel engines and lean-burn engines are characterized by up to 20% lower fuel consumption.
- a major problem of these motors is the cleaning of their exhaust gases. Because of the high oxygen content in the exhaust gas of up to 15 vol .-% can indeed the oxidizable pollutant components of the exhaust gas (hydrocarbons HC, carbon monoxide CO and small amounts of hydrogen H2) slightly convert a catalyst to carbon dioxide and water, but the nitrogen oxides NO x that also arise during the combustion of the fuel cannot, however, be reduced to nitrogen N 2 to a sufficient extent because of the preferred oxidation reactions.
- the selective catalytic reduction with ammonia shows So very good results, but with a significant one equipment expenditure, the use of smaller Has prevented engines so far. It is therefore the job of present invention, a method for selective catalytic Specify reduction with ammonia, which is by simply generating what is required for the reduction Ammoniaks distinguished.
- the air ratio ( ⁇ ) describes the composition of the gas flow. It is the stoichiometric one Conditioned air / fuel ratio. Stoichiometric Conditions exist for an air ratio of 1. If the air ratio is above 1, the gas contains more oxygen than for a complete combustion of the flammable Components is needed. Such a gas composition is called lean. A rich gas composition is present when the oxygen content is lower than for a complete combustion of all combustible components of the gas is needed.
- ⁇ ⁇ 1 sub-stoichiometric air / fuel mixture
- the rich gas flow can also be part of the Exhaust gas from the internal combustion engine can be obtained by a Cylinder of the machine with a substoichiometric Air / fuel mixture is operated. Still exists the ability to inject the rich gas stream by injecting Form hydrocarbons in an air stream.
- a rich exhaust gas contains, for example, carbon monoxide, nitrogen monoxide and water vapor in addition to unburned hydrocarbons.
- Ammonia can be formed from the latter three substances according to the following reaction equation: 5CO + 2NO + 3H 2 O -> 5CO 2 + 2NH 3
- Nitrogen monoxide therefore becomes ammonia using carbon monoxide reduced.
- the formation of ammonia is not one Reaction control according to the gross reaction equation given above limited.
- hydrogen with nitrogenous gas components respectively be converted to ammonia with nitrogen.
- ammonia can occur in several ways be made. There is a possibility of the above Reaction going on just by thermal activation set, that is, by heating the rich exhaust gas. However, the back reaction also increases with increasing temperature to. Reaction pathways are therefore more favorable which the exhaust gas does not have to be heated thermally. On An example of this is the implementation of the reaction on one suitable catalyst. The catalytic reaction is needed usually lower temperatures, reducing the influence the back reaction can be reduced.
- ammonia in a rich gas stream also when passing through an electrical gas discharge plasma is formed.
- the formation of ammonia in one electrical gas discharge is thermodynamically favored, because they are at much lower temperatures than that catalytic reduction expires.
- Figure 1 shows the formation of ammonia and nitrogen monoxide by thermal cleavage of cetane (C 8 H 18 ).
- the formation of ammonia decreases with increasing temperature.
- the formation of nitrogen monoxide increases sharply above 600 ° C.
- An electrical one is preferred for the formation of ammonia Gas discharge used.
- are mixed forms of these electrical gas discharges. are preferred for the proposed method Barrier discharges used.
- a barrier discharge can occur between two metallic ones Electrodes are generated, at least one with one Dielectric is occupied, which is a spark or arcing prevented between the two metallic electrodes. Instead, a large number of short-term forms and spatially limited micro-discharges, whose Discharge time and amount of energy through the dielectric is limited.
- Suitable dielectrics are ceramics, glass, Porcelain or insulating plastics such as Teflon.
- Barrier discharges can occur at pressures between 0.1 and 10 bar can be operated.
- the electrical excitation of the discharge is done by applying an AC voltage to the Electrodes.
- the distance of the Form electrodes, frequency and amplitude of the AC voltage become thin, spatially when an ignition voltage is exceeded and temporally distributed discharge channels lasting only a few nanoseconds.
- FIG. 2 shows the basic structure of a plasma reactor, in which a dielectric barrier discharge is ignited can be.
- (2) and (3) denote two metallic ones Electrodes that face each other and with an AC voltage source (5) are connected.
- a dielectric (4) is covered with a dielectric (4).
- Such a discharge is hindered as dielectric on one side designated.
- the voltage required depends on the free distance d between dielectric and counter electrode, from the used Dielectric and the pressure in the discharge path, of the gas composition and any existing Installation between the dielectrics in the discharge space from.
- the distance d is preferably between 0.1 and 10 mm set.
- the required voltages can range from 0.2 to 15 amount to kV.
- the frequency of the AC voltage can be between 50 Hz and 250 kHz can be selected. These AC voltages can also with low frequency (10 to 0.01 Hz) clocked operated, for example, the reaction of adsorbed species.
- Figure 3 shows a modification of the arrangement of Figure 2.
- both electrodes are covered with a dielectric.
- the gas discharge that forms in the discharge space is therefore referred to as dielectrically impeded on both sides.
- FIG. 4 shows a particularly advantageous embodiment of the Plasma reactor.
- the discharge space is filled with pellets.
- the pellets can be made of catalytically active materials or Materials with special chemical properties or Surface properties exist. Also inert ceramic Balls have a positive influence on the formation of the electrical discharge. Which is in one with pellets filled reactor forming electrical discharge takes place especially in the form of sliding discharges on the Surface of the pellets instead. This will increase concentration of ions and radicals in the vicinity of the Surface increased.
- catalytic Active pellets can form ammonia in the gas discharge be promoted.
- the catalytically active pellets preferably consist of at least one finely divided support material selected from the group consisting of aluminum oxide, titanium oxide, zirconium oxide, cerium oxide, silicon dioxide, magnesium oxide or their mixed oxides and zeolites.
- the carrier materials can be stabilized in a known manner with silicon dioxide and / or rare earth oxides against thermal loads.
- they can be catalytically activated on their surface in a highly disperse form by depositing at least one of the platinum group noble metals, in particular platinum, palladium, rhodium and iridium.
- the specific surface area of the carrier materials should be at least 10 m 2 / g (measured according to DIN 66132). It is also advantageous if the ceramic pellets additionally contain at least one basic oxide of the alkali or alkaline earth metals of the periodic table of the elements.
- the dielectric on the electrode surfaces with a catalytic active layer made of finely divided carrier materials and catalytically active components.
- Your Composition can be the one just described Composition to match the ceramic pellets.
- the dielectric can be applied to the Electrode surfaces themselves as a catalytically active layer made of finely divided carrier materials and catalytically active Components be formed. The prerequisite for this is that the insulation effect of the layer meets the requirements a dielectric barrier discharge is sufficient.
- the electrodes of the plasma reactor can be considered parallel to each other aligned flat structures can be built up or of two concentrically arranged Tube electrodes are formed, the electrical Discharge in the space between the two Electrodes expires.
- the reactor from two parallel plate electrodes is at least one of the Electrodes on the opposite surfaces with coated with a dielectric.
- concentric arranged tubular electrodes is at least one of the Electrodes on the opposing jacket surfaces coated with a dielectric.
- the discharge can take place via various types of alternating voltages be stimulated.
- alternating voltages For a high electron density and if possible simultaneous formation of the discharge throughout Discharge space of the reactor are pulsed excitation voltages with a frequency between 50 Hz and 250 kHz particularly suitable.
- the reactor can be any electrically and thermally suitable Material are made.
- plastics are To name ceramics and glasses. Are also hybrid Constructions made of different materials possible.
- US 5,116,586 discloses an SCR catalyst on the Base of zeolite based on a zeolite of the mordenite type Contains copper, iron, molybdenum, cerium or mixtures thereof.
- SCR catalysts which catalytically active component at least one platinum group metal in highly disperse form on a suitable carrier material contain.
- Magnesium oxide, Aluminum oxides, silicon oxide, titanium oxide, zirconium oxide and their mixtures are used.
- the catalysts mentioned can be in the form of pellets present or to monolithic structures, in particular Honeycomb bodies, extruded. Can also be used So-called coating catalysts, in which the catalyst in the form of a layer on an inert support body is applied.
- the proposed method is intended to reduce the nitrogen oxides in oxygen-rich that is, in lean exhaust gases by selective Reduce catalytic reduction with ammonia.
- the ammonia becomes a fat, low-oxygen Gas flow, for example in the form of a partial exhaust gas flow needed.
- FIG. 5 shows an internal combustion engine (10) with 4 cylinders (11).
- the engine runs on a lean air / fuel mixture operated, that is, the air ratio ⁇ is greater than 1 ( ⁇ > 1). Because of the combustion in the machine Air ratio is not changed, also shows the exhaust gas Machine has an air ratio of over 1.
- the lean exhaust gas from the four cylinders is in the exhaust pipe (12) summarized and only over a catalyst for the selective reduction (13) and then over an oxidation catalyst (14) headed.
- the oxidation catalyst (14) is optional. It should be used in the event of a possible overdose of ammonia oxidize it and thus an emission of Prevent ammonia.
- FIG an additional burner (15) is provided with a sub-stoichiometric air / fuel mixture ( ⁇ ⁇ 1) operated becomes. This can advantageously be done in the vehicle existing parking heater can be used. Such Auxiliary heating is often used in the fuel-saving models considered here Vehicles necessary to the passenger compartment to heat.
- the exhaust gas from the burner is used to form Ammonia from the electrical gas discharge of a plasma reactor (16) passed and then in front of the catalyst for the selective catalytic reduction of the exhaust gas Internal combustion engine added.
- Reference numeral (17) shows ba the electrodes of the plasma reactor.
- the auxiliary heater fulfills the purpose of additional heating the passenger compartment, on the other hand it provides an easily controllable component for generating a fat Exhaust gas partial flow.
- a heat exchanger can be installed to cool the exhaust gas.
- the heating efficiency is only due to the slightly greasy mode of operation, but not through heat energy extraction, reduced.
- FIG. 6 shows another way of generating a rich exhaust gas partial flow.
- (10) also denotes here the internal combustion engine with four cylinders (11) and (11 '). In this case it is a direct injection Gasoline or diesel engine with controllable injection for each cylinder.
- the cylinders (11) are with a lean air / fuel mixture ( ⁇ > 1) and cylinder (11 ') operated with a rich air / fuel mixture ( ⁇ ⁇ 1).
- the plasma reactor (16) for generating ammonia.
- the two process steps generation of a rich gas stream and ammonia formation
- This can be done, for example, by injecting Fuel along with a substoichiometric amount Air happen in the plasma reactor.
- Figure 7 shows a coaxial plasma reactor. (20) an outer tube and (21) an inner tube made of quartz glass. The Inner surface of the inner tube and the outer surface of the outer tube are covered with metallic electrodes (23) and (22). By applying a voltage source (24) to this Electrodes can be in the annular space between Inner tube and outer tube a dielectric barrier discharge be ignited.
- FIG. 8 shows the cross section through a honeycomb structure Reactor perpendicular to the flow channels (33) for the exhaust gas.
- the honeycomb alternately consists of layers of smooth (31) and corrugated (30) metal foils that are coated on both sides with a dielectric (32).
- the smooth sheets are common across an electrical Line with one pole of the high voltage source (34) and the corrugated foils with the second pole of the voltage source connected. Applying a voltage finds an electrical one Discharge transversely in each flow channel (33) to the flow of the exhaust gas instead.
- the coating of the Metal foils with the dielectric isolate the neighboring ones Foils electrically against each other. It can be either smooth or corrugated or both types of film with one Dielectric for mutual electrical insulation be coated. Instead of the dielectric coating there is the possibility of a dielectric interlayer between adjacent foils. With this intermediate layer for example, it can be a ceramic one Trade slide.
- the length of the honeycomb body is not limited.
- Figure 8 there are corrugated and smooth metal foils combined with each other and form a stack of films. It can also use two differently corrugated metal foils can be combined with each other.
- the type of curl, as well as the cross-sectional dimensions of the flow channels can be adapted to the application requirements.
- the dielectric layers which the metal foils against the gas discharge and each other isolate a catalyst layer made of fine particles Carrier materials and catalytically active components be applied.
- the dielectric layers themselves as catalytically active Layer of finely divided carrier materials and catalytic active components if this layer a the requirements of dielectric barrier discharge has sufficient insulation effect.
- the composition this catalytically active layer can for the composition described for the ceramic pellets correspond.
- the proposed method has compared to the known Procedure various advantages. For example it is applicable to different engine concepts. When using Lean engines worsen consumption values for the fuel only slightly. It is particularly advantageous the generation of ammonia on board the motor vehicle without the need to carry additional supplies have to. The necessary amount of ammonia can be over electrical and geometric parameters of gas discharge as well as the provision of the rich exhaust gas partial flow can be set. The control of this process can be carried out by the engine electronics.
- the coaxial reactor of FIG. 7 was used for plasma discharge.
- the outer and inner tubes consisted of 2 mm thick Quartz glass.
- the outer tube had an outer diameter of 4 and the inner tube has an inner diameter of 2.6 cm.
- the Length of the reactor was 20 and the length of the electrodes 16 cm.
- the gas discharge space between the two quartz tubes was with a palladium pellet catalyst (3.2 g Palladium and 35 g of barium oxide on a liter of pellets ⁇ -aluminum oxide) filled.
- the synthesis gas mixture in Table 1 is lean, which means that it has an over-stoichiometric oxygen content (the air ratio ⁇ is greater than 1.). Under these conditions, nitrogen monoxide is adsorbed by the pellet catalyst when the gas discharge is switched on. Be explained - may be caused by the conversion of NO to NO 2 in the plasma reactor at excess air and subsequent further oxidation and storage as NO. 3 If a switch is made from the lean exhaust gas composition to a rich composition, the previously adsorbed nitrogen monoxide is desorbed. At the same time, ammonia is formed in the gas discharge, which very effectively converts the desorbed nitrogen oxide into nitrogen and water.
- FIG. 9 shows the course of the concentration of nitrogen monoxide depending on the synthesis gas behind the plasma reactor of the electrical coupled into the gas discharge Power.
- the gas discharge is switched off (electrical Performance 0) is the NO concentration behind the plasma reactor according to the synthesis gas mixture of 500 ppm Table 1 measured.
- the gas discharge After switching on the gas discharge immediately finds a sharp reduction in the NO concentration instead of. This is due to the formation of nitrogen dioxide attributed to the plasma discharge, which is very effective is adsorbed by the catalyst pellets.
- FIG. 9 shows after the switching of the exhaust gas composition a strong desorption of nitrogen monoxide under the reducing exhaust gas conditions now present.
- ammonia is formed by the plasma discharge using nitrogen monoxide and possibly further nitrogen-containing compounds of the gas stream (for example N 2 ).
- Figures 10 to 12 show spectroscopic examinations of the exhaust gas during the lean operating phase, during the Switching from lean to rich mode and during the fat operating phase. Shows during the lean phase the exhaust gas only the absorption bands of nitrogen monoxide. These absorption bands disappear during the switching phase ( Figure 11) and during the rich operating phase the exhaust gas clearly shows the absorption bands of the formed Ammoniaks ( Figure 12).
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Abstract
Description
Die Erfindung betrifft ein Verfahren zur selektiven katalytischen Reduktion der in einem mageren Abgas von Verbrennungsmotoren enthaltenen Stickoxide durch Reduktion der Stickoxide mittels Ammoniak an einem Katalysator.The invention relates to a method for selective catalytic Reduction in lean exhaust gas from internal combustion engines contained nitrogen oxides by reducing the Nitrogen oxides using ammonia on a catalyst.
Bei den Verbrennungsmotoren mit magerem Abgas handelt es sich um Dieselmotoren und mager betriebene Benzinmotoren, sogenannte Magermotoren. Gegenüber stöchiometrisch betriebenen konventionellen Motoren zeichnen sich Dieselmotoren und Magermotoren durch einen um bis zu 20% geringeren Kraftstoffverbrauch aus. Ein wesentliches Problem dieser Motoren stellt die Reinigung ihrer Abgase dar. Wegen des hohen Sauerstoffgehaltes im Abgas von bis zu 15 Vol.-% lassen sich zwar die oxidierbaren Schadstoffkomponenten des Abgases (Kohlenwasserstoffe HC, Kohlenmonoxid CO und in geringen Mengen Wasserstoff H2) leicht an einem Katalysator zu Kohlendioxid und Wasser umsetzen, die bei der Verbrennung des Kraftstoffs jedoch ebenfalls entstehenden Stickoxide NOX können aber wegen der bevorzugt ablaufenden Oxidationsreaktionen nicht im ausreichenden Maße zu Stickstoff N2 reduziert werden.The internal combustion engines with lean exhaust gas are diesel engines and lean petrol engines, so-called lean-burn engines. Compared to stoichiometrically operated conventional engines, diesel engines and lean-burn engines are characterized by up to 20% lower fuel consumption. A major problem of these motors is the cleaning of their exhaust gases. Because of the high oxygen content in the exhaust gas of up to 15 vol .-% can indeed the oxidizable pollutant components of the exhaust gas (hydrocarbons HC, carbon monoxide CO and small amounts of hydrogen H2) slightly convert a catalyst to carbon dioxide and water, but the nitrogen oxides NO x that also arise during the combustion of the fuel cannot, however, be reduced to nitrogen N 2 to a sufficient extent because of the preferred oxidation reactions.
Zur Lösung dieses Problems wurde das schon bei stationären Verbrennungsanlagen bekannte Verfahren der selektiven katalytischen Reduktion SCR (Selective Catalytic Reduction) vorgeschlagen. Hierbei wird dem mageren Abgas ein Reduktionsmittel zugeführt, mit dessen Hilfe die Stickoxide an einem hierfür geeigneten Katalysator selektiv reduziert werden können. Bevorzugt wird als Reduktionsmittel Ammoniak verwendet, welches mit hoher Selektivität mit den Stickoxiden zu Stickstoff und Wasser reagiert. Das Verhältnis von eingebrachtem Ammoniak zu den vorhandenen Stickoxiden ist etwa 1:1. Ammoniak kann dabei direkt aus Harnstoff mit Hilfe eines Hydrolysekatalysators oder durch Zersetzung eines entsprechenden Salzes (z.B. Carbamate) erzeugt werden.This has already been solved for stationary in order to solve this problem Incinerators known methods of selective catalytic Reduction SCR (Selective Catalytic Reduction) suggested. Here, the lean exhaust gas becomes a reducing agent supplied, with the help of the nitrogen oxides selectively reduced a suitable catalyst can be. Ammonia is preferred as the reducing agent used, which with high selectivity with the nitrogen oxides reacted to nitrogen and water. The ratio of introduced ammonia to the existing nitrogen oxides about 1: 1. Ammonia can be made directly from urea With the help of a hydrolysis catalyst or by decomposition of an appropriate salt (e.g. carbamates) become.
Zur Zeit werden große Anstrengungen unternommen, solche Systeme in Lastkraftwagen einzusetzen. Nachteilig bei diesem Verfahren ist, daß ein weiterer Betriebsstoff mitgeführt werden muß. Der mit der SCR-Technologie verbundene hohe Aufwand hat bisher ihren breiten Einsatz insbesondere bei Personenkraftwagen verhindert. Alternativ zu Ammoniak können als Reduktionsmittel auch Alkohole, Wasserstoff oder Kohlenwasserstoffe eingesetzt werden. Diese Reduktionsmittel weisen jedoch deutlich schlechtere Selektivitäten für die Stickoxidreduktion im mageren Abgas als Ammoniak auf. So zeigt sich über gesetzlich vorgeschriebene Fahrzyklen mit den alternativen Reduktionsmitteln ein Stickoxidumsatz von bis zu 30%, während mit Ammoniak Umsätze bis über 70% möglich sind.Great efforts are currently being put into such systems used in trucks. A disadvantage of this The procedure is that another fuel is carried must become. The high associated with SCR technology So far, effort has been particularly widespread Passenger cars prevented. As an alternative to ammonia can also be used as reducing agents alcohols, hydrogen or Hydrocarbons are used. These reducing agents however, have significantly poorer selectivities for the nitrogen oxide reduction in the lean exhaust gas than ammonia. This shows how legally prescribed driving cycles are nitrogen oxide conversion with the alternative reducing agents up to 30%, while with ammonia sales up to 70% possible are.
Die selektive katalytische Reduktion mit Ammoniak zeigt also sehr gute Ergebnisse, ist jedoch mit einem erheblichen apparativen Aufwand verbunden, der den Einsatz an kleineren Motoren bisher verhindert hat. Es ist daher Aufgabe der vorliegenden Erfindung, ein Verfahren zur selektiven katalytischen Reduktion mit Ammoniak anzugeben, welches sich durch eine einfache Erzeugung des für die Reduktion benötigten Ammoniaks auszeichnet.The selective catalytic reduction with ammonia shows So very good results, but with a significant one equipment expenditure, the use of smaller Has prevented engines so far. It is therefore the job of present invention, a method for selective catalytic Specify reduction with ammonia, which is by simply generating what is required for the reduction Ammoniaks distinguished.
Diese Aufgabe wird gelöst durch ein Verfahren zur selektiven
katalytischen Reduktion der in einem mageren Abgas
von Verbrennungskraftmaschinen mit einem oder mehreren Zylindern
enthaltenen Stickoxide durch Reduktion der Stickoxide
mittels Ammoniak an einem Reduktions-Katalysator. Das
Verfahren ist gekennzeichnet durch die Verfahrensschritte:
Die Luftzahl (λ) beschreibt die Zusammensetzung des Gasstromes. Es handelt sich dabei um das auf stöchiometrische Bedingungen normierte Luft/Kraftstoff-Verhältnis. Stöchiometrische Bedingungen liegen bei einer Luftzahl von 1 vor. Bei einer Luftzahl über 1 enthält das Gas mehr Sauerstoff als für eine vollständige Verbrennung der brennbaren Bestandteile benötigt wird. Eine solche Gaszusammensetzung wird als mager bezeichnet. Eine fette Gaszusammensetzung liegt vor, wenn der Sauerstoffgehalt geringer ist als für eine vollständige Verbrennung aller brennbaren Bestandteile des Gases benötigt wird.The air ratio (λ) describes the composition of the gas flow. It is the stoichiometric one Conditioned air / fuel ratio. Stoichiometric Conditions exist for an air ratio of 1. If the air ratio is above 1, the gas contains more oxygen than for a complete combustion of the flammable Components is needed. Such a gas composition is called lean. A rich gas composition is present when the oxygen content is lower than for a complete combustion of all combustible components of the gas is needed.
Wesentlich für das erfindungsgemäße Verfahren ist die Erzeugung des für die katalytische Reduktion benötigten Ammoniaks aus einem fetten Gasstrom durch Reaktion seiner Komponenten untereinander. Ein solcher Gasstrom kann zum Beispiel durch einen Brenner erzeugt werden, der mit einem unterstöchiometrischen Luft/Kraftstoff-Gemisch (λ < 1) betrieben wird. Der fette Gasstrom kann auch als ein Teil des Abgases der Verbrennungsmaschine gewonnen werden, indem ein Zylinder der Maschine mit einem unterstöchiometrischen Luft/Kraftstoff-Gemisch betrieben wird. Weiterhin besteht die Möglichkeit, den fetten Gasstrom durch Einspritzen von Kohlenwasserstoffen in einen Luftstrom zu bilden.Generation is essential for the method according to the invention of the ammonia required for the catalytic reduction from a rich gas stream by reaction of its components among themselves. Such a gas flow can Example generated by a burner with a sub-stoichiometric air / fuel mixture (λ <1) operated becomes. The rich gas flow can also be part of the Exhaust gas from the internal combustion engine can be obtained by a Cylinder of the machine with a substoichiometric Air / fuel mixture is operated. Still exists the ability to inject the rich gas stream by injecting Form hydrocarbons in an air stream.
Ein fettes Abgas enthält zum Beispiel neben unverbrannten
Kohlenwasserstoffen noch Kohlenmonoxid, Stickstoffmonoxid
und Wasserdampf. Aus den letzteren drei Stoffen läßt sich
Ammoniak nach folgender Reaktionsgleichung bilden:
Stickstoffmonoxid wird also mittels Kohlenmonoxid zu Ammoniak reduziert. Die Bildung von Ammoniak ist nicht auf eine Reaktionsführung gemäß der oben angegebenen Bruttoreaktionsgleichung beschränkt. Ebenso kann zum Beispiel Wasserstoff mit stickstoffhaltigen Gaskomponenten beziehungsweise mit Stickstoff zu Ammoniak umgesetzt werden.Nitrogen monoxide therefore becomes ammonia using carbon monoxide reduced. The formation of ammonia is not one Reaction control according to the gross reaction equation given above limited. Likewise, for example, hydrogen with nitrogenous gas components respectively be converted to ammonia with nitrogen.
Die Bildung von Ammoniak kann auf verschiedene Weise vorgenommen werden. Es besteht die Möglichkeit, die obige Reaktion allein durch thermische Aktivierung in Gang zu setzen, das heißt durch Aufheizen des fetten Abgases. Allerdings nimmt mit zunehmender Temperatur auch die Rückreaktion zu. Günstiger sind deshalb Reaktionswege, bei denen das Abgas nicht thermisch aufgeheizt werden muß. Ein Beispiel hierfür ist die Durchführung der Reaktion an einem geeigneten Katalysator. Die katalytische Reaktion benötigt in der Regel geringere Temperaturen, wodurch der Einfluß der Rückreaktion vermindert werden kann.The formation of ammonia can occur in several ways be made. There is a possibility of the above Reaction going on just by thermal activation set, that is, by heating the rich exhaust gas. However, the back reaction also increases with increasing temperature to. Reaction pathways are therefore more favorable which the exhaust gas does not have to be heated thermally. On An example of this is the implementation of the reaction on one suitable catalyst. The catalytic reaction is needed usually lower temperatures, reducing the influence the back reaction can be reduced.
Es wurde gefunden, daß Ammoniak in einem fetten Gasstrom auch beim Durchleiten durch ein elektrisches Gasentladungsplasma gebildet wird. Die Bildung von Ammoniak in einer elektrischen Gasentladung ist thermodynamisch begünstigt, da sie bei noch wesentlich niedrigeren Temperaturen als die katalytische Reduktion abläuft.It has been found that ammonia in a rich gas stream also when passing through an electrical gas discharge plasma is formed. The formation of ammonia in one electrical gas discharge is thermodynamically favored, because they are at much lower temperatures than that catalytic reduction expires.
Die Erfindung wird im folgenden an Hand der Figuren 1 bis 9 näher erläutert. Es zeigen:
- Figur 1:
- Bildung von Ammoniak und Stickstoffmonoxid durch thermische Spaltung von Cetan (C8H18).
- Figur 2:
- Dielektrische Barrieren-Entladung mit parallelen, flächigen Elektroden; einseitig dielektrisch behinderte Entladung
- Figur 3:
- Dielektrische Barrieren-Entladung mit parallelen, flächigen Elektroden; beidseitig dielektrisch behinderte Entladung
- Figur 4:
- Dielektrische Barrieren-Entladung mit parallelen, flächigen Elektroden; beidseitig dielektrisch behindert; mit Pellets gefüllter Entladungsraum
- Figur 5:
- Verbrennungskraftmaschine mit zusätzlichem, unterstöchiometrischen Brenner zur Erzeugung eines fetten Abgas-Teilstroms
- Figur 6:
- Verbrennungskraftmaschine mit getrennter Ansteuerung der Zylinder zur Erzeugung eines fetten Abgas-Teilstroms
- Figur 7:
- Koaxialer Reaktor mit Palladium-Pelletkatalysator
- Figur 8:
- Reaktor mit wabenförmigem Aufbau
- Figur 9:
- NOX-Konzentration im emittierten Abgas in Abhängigkeit von der elektrischen Leistung der Gasentladung und der Luftzahl des Abgases
- Figur 10:
- Absorptionsbanden von Stickstoffmonoxid in der mageren Synthesegasmischung nach Durchströmen des Plasmareaktors bei abgeschalteter Gasentladung
- Figur 11:
- Absorptionsspektrum der Synthesegasmischung nach Durchlaufen des Plasmareaktors zum Zeitpunkt des Umschaltens von magerer auf fette Gaszusammensetzung
- Figur 12:
- Absorptionsbanden von Ammoniak in der fetten Synthesegasmischung nach Durchströmen des Plasmareaktors bei laufender Gasentladung
- Figure 1:
- Formation of ammonia and nitrogen monoxide by thermal cleavage of cetane (C 8 H 18 ).
- Figure 2:
- Dielectric barrier discharge with parallel, flat electrodes; Discharged discharge on one side
- Figure 3:
- Dielectric barrier discharge with parallel, flat electrodes; Discharged discharge on both sides
- Figure 4:
- Dielectric barrier discharge with parallel, flat electrodes; dielectrically impeded on both sides; Discharge room filled with pellets
- Figure 5:
- Internal combustion engine with an additional, substoichiometric burner for generating a rich partial exhaust gas flow
- Figure 6:
- Internal combustion engine with separate control of the cylinders to generate a rich partial exhaust gas flow
- Figure 7:
- Coaxial reactor with palladium pellet catalyst
- Figure 8:
- Honeycomb-shaped reactor
- Figure 9:
- NO x concentration in the emitted exhaust gas as a function of the electrical power of the gas discharge and the air ratio of the exhaust gas
- Figure 10:
- Absorption bands of nitrogen monoxide in the lean synthesis gas mixture after flowing through the plasma reactor with the gas discharge switched off
- Figure 11:
- Absorption spectrum of the synthesis gas mixture after passing through the plasma reactor at the time of switching from lean to rich gas composition
- Figure 12:
- Absorption bands of ammonia in the rich synthesis gas mixture after flowing through the plasma reactor while the gas discharge is running
Figur 1 zeigt die Bildung von Ammoniak und Stickstoffmonoxid durch thermische Spaltung von Cetan (C8H18). Die dargestellten Kurven sind das Ergebnis thermodynamischer Berechnungen für zwei verschiedene Luftzahlen (λ = 0,984) und (λ = 0,992) des angenommenen Gasgemisches. Mit zunehmender Temperatur fällt die Bildung von Ammoniak ab. Gleichzeitig nimmt die Bildung von Stickstoffmonoxid oberhalb von 600°C stark zu.Figure 1 shows the formation of ammonia and nitrogen monoxide by thermal cleavage of cetane (C 8 H 18 ). The curves shown are the result of thermodynamic calculations for two different air numbers (λ = 0.984) and (λ = 0.992) of the assumed gas mixture. The formation of ammonia decreases with increasing temperature. At the same time, the formation of nitrogen monoxide increases sharply above 600 ° C.
Bevorzugt wird für die Bildung von Ammoniak eine elektrische Gasentladung eingesetzt. Geeignet sind zum Beispiel Mikrowellenentladungen, auch mit Frequenzen oberhalb 250 MHz, Coronaentladungen und die dielektrisch behinderte Entladung, auch Barrieren-Entladung genannt. Ebenso geeignet sind Mischformen dieser elektrischen Gasentladungen. Bevorzugt werden für das vorgeschlagene Verfahren Barrieren-Entladungen eingesetzt.An electrical one is preferred for the formation of ammonia Gas discharge used. For example, are suitable Microwave discharges, also with frequencies above 250 MHz, corona discharges and the dielectric barrier Discharge, also called barrier discharge. Also suitable are mixed forms of these electrical gas discharges. Are preferred for the proposed method Barrier discharges used.
Eine Barrieren-Entladung kann zwischen zwei metallischen Elektroden erzeugt werden, von denen wenigsten eine mit einem Dielektrikum belegt ist, das eine Funken- oder Bogenbildung zwischen den beiden metallischen Elektroden verhindert. Stattdessen bildet sich eine Vielzahl von kurzzeitigen und räumlich eng begrenzten Mikroentladungen aus, deren Entladungsdauer und Energiemenge durch das Dielektrikum begrenzt wird. Geeignete Dielektrika sind Keramiken, Glas, Porzellan oder isolierende Kunststoffe wie zum Beispiel Teflon.A barrier discharge can occur between two metallic ones Electrodes are generated, at least one with one Dielectric is occupied, which is a spark or arcing prevented between the two metallic electrodes. Instead, a large number of short-term forms and spatially limited micro-discharges, whose Discharge time and amount of energy through the dielectric is limited. Suitable dielectrics are ceramics, glass, Porcelain or insulating plastics such as Teflon.
Barrieren-Entladungen können bei Drücken zwischen 0,1 und 10 bar betrieben werden. Die elektrische Anregung der Entladung erfolgt durch Anlegen einer Wechselspannung an die Elektroden. Je nach Druck im Entladungsraum, Abstand der Elektroden, Frequenz und Amplitude der Wechselspannung bilden sich beim Überschreiten einer Zündspannung dünne, räumlich und zeitlich statistisch verteilte Entladungskanäle von nur wenigen Nanosekunden Dauer aus. Barrier discharges can occur at pressures between 0.1 and 10 bar can be operated. The electrical excitation of the discharge is done by applying an AC voltage to the Electrodes. Depending on the pressure in the discharge space, the distance of the Form electrodes, frequency and amplitude of the AC voltage become thin, spatially when an ignition voltage is exceeded and temporally distributed discharge channels lasting only a few nanoseconds.
Figur 2 zeigt den prinzipiellen Aufbau eines Plasmareaktors, in dem eine dielektrische Barrieren-Entladung gezündet werden kann. (2) und (3) bezeichnen zwei metallische Elektroden, die sich gegenüberstehen und mit einer Wechselspannungsquelle (5) verbunden sind. Zur Unterbindung der Ausbildung eines Entladungsbogens zwischen den beiden Elektroden ist Elektrode (2) mit einem Dielektrikum (4) belegt. Eine solche Entladung wird als einseitig dielektrisch behindert bezeichnet.FIG. 2 shows the basic structure of a plasma reactor, in which a dielectric barrier discharge is ignited can be. (2) and (3) denote two metallic ones Electrodes that face each other and with an AC voltage source (5) are connected. To prevent the Formation of a discharge arc between the two electrodes electrode (2) is covered with a dielectric (4). Such a discharge is hindered as dielectric on one side designated.
Durch Anlegen einer Wechselspannung an die beiden Elektroden kommt es bei ausreichender Spannung zu der gewünschten Entladung. Die benötigte Spannung hängt von dem freien Abstand d zwischen Dielektrikum und Gegenelektrode, vom verwendeten Dielektrikum sowie vom Druck in der Entladungsstrecke, von der Gaszusammensetzung und von eventuell vorhandenen Einbauten zwischen den Dielektrika im Entladungsraum ab. Der Abstand d wird bevorzugt zwischen 0,1 und 10 mm eingestellt. Die benötigten Spannungen können 0,2 bis 15 kV betragen. Die Frequenz der Wechselspannung kann zwischen 50 Hz und 250 kHz gewählt werden. Diese Wechselspannungen können auch mit niedriger Frequenz (10 bis 0,01 Hz) getaktet betrieben werden, um beispielsweise die Reaktion von adsorbierten Spezies zu ermöglichen.By applying an alternating voltage to the two electrodes if there is sufficient voltage, the desired result Discharge. The voltage required depends on the free distance d between dielectric and counter electrode, from the used Dielectric and the pressure in the discharge path, of the gas composition and any existing Installation between the dielectrics in the discharge space from. The distance d is preferably between 0.1 and 10 mm set. The required voltages can range from 0.2 to 15 amount to kV. The frequency of the AC voltage can be between 50 Hz and 250 kHz can be selected. These AC voltages can also with low frequency (10 to 0.01 Hz) clocked operated, for example, the reaction of adsorbed species.
Figur 3 zeigt eine Abwandlung der Anordnung von Figur 2. In Figur 3 sind beide Elektroden mit einem Dielektrikum belegt. Die sich im Entladungsraum ausbildende Gasentladung wird deshalb als beidseitig dielektrisch behindert bezeichnet.Figure 3 shows a modification of the arrangement of Figure 2. In Figure 3, both electrodes are covered with a dielectric. The gas discharge that forms in the discharge space is therefore referred to as dielectrically impeded on both sides.
Figur 4 zeigt eine besonders vorteilhafte Ausbildung des Plasmareaktors. Der Entladungsraum ist mit Pellets gefüllt. Die Pellets können aus katalytisch aktiven Materialien oder Materialien mit besonderen chemischen Eigenschaften oder Oberflächeneigenschaften bestehen. Auch inerte keramische Kugeln haben einen positiven Einfluß auf die Ausbildung der elektrischen Entladung. Die sich in einem mit Pellets gefüllten Reaktor ausbildende elektrische Entladung findet vor allen Dingen in Form von Gleitentladungen an der Oberfläche der Pellets statt. Dadurch wird die Konzentration an Ionen und Radikalen in räumlicher Nachbarschaft der Oberfläche erhöht. Durch die Verwendung von katalytisch aktiven Pellets kann die Bildung von Ammoniak in der Gasentladung gefördert werden.Figure 4 shows a particularly advantageous embodiment of the Plasma reactor. The discharge space is filled with pellets. The pellets can be made of catalytically active materials or Materials with special chemical properties or Surface properties exist. Also inert ceramic Balls have a positive influence on the formation of the electrical discharge. Which is in one with pellets filled reactor forming electrical discharge takes place especially in the form of sliding discharges on the Surface of the pellets instead. This will increase concentration of ions and radicals in the vicinity of the Surface increased. By using catalytic Active pellets can form ammonia in the gas discharge be promoted.
Die katalytisch aktiven Pellets bestehen bevorzugt aus mindestens einem feinteiligen Trägermaterial ausgewählt aus der Gruppe Aluminiumoxid, Titanoxid, Zirkonoxid, Ceroxid, Siliciumdioxid, Magnesiumoxid oder deren Mischoxide und Zeolithen. Die Trägermaterialien können in bekannter Weise mit Siliciumdioxid und/oder Seltenerdoxiden gegenüber thermischen Belastungen stabilisiert sein. Außerdem können sie durch Abscheiden mindestens eines der Edelmetalle der Platingruppe, insbesondere Platin, Palladium, Rhodium und Iridium, in hochdisperser Form auf ihre Oberfläche katalytisch aktiviert werden. Zu diesem Zweck sollte die spezifische Oberfläche der Trägermaterialien wenigstens 10 m2/g (gemessen nach DIN 66132) betragen. Weiterhin ist es vorteilhaft, wenn die keramischen Pellets zusätzlich mindestens ein basisches Oxid der Alkali- oder Erdalkalimetalle des Periodensystems der Elemente enthalten.The catalytically active pellets preferably consist of at least one finely divided support material selected from the group consisting of aluminum oxide, titanium oxide, zirconium oxide, cerium oxide, silicon dioxide, magnesium oxide or their mixed oxides and zeolites. The carrier materials can be stabilized in a known manner with silicon dioxide and / or rare earth oxides against thermal loads. In addition, they can be catalytically activated on their surface in a highly disperse form by depositing at least one of the platinum group noble metals, in particular platinum, palladium, rhodium and iridium. For this purpose, the specific surface area of the carrier materials should be at least 10 m 2 / g (measured according to DIN 66132). It is also advantageous if the ceramic pellets additionally contain at least one basic oxide of the alkali or alkaline earth metals of the periodic table of the elements.
Zusätzlich zu den Pellets oder alternativ dazu kann das Dielektrikum auf den Elektrodenoberflächen mit einer katalytisch aktiven Schicht aus feinteiligen Trägermaterialien und katalytisch aktiven Komponenten versehen sein. Ihre Zusammensetzung kann der soeben beschriebenen Zusammensetzung für die keramischen Pellets entsprechen. In bestimmten Anwendungsfällen kann das Dielektrikum auf den Elektrodenoberflächen selbst als katalytisch aktive Schicht aus feinteiligen Trägermaterialien und katalytisch aktiven Komponenten ausgebildet sein. Voraussetzung hierfür ist, daß die Isolationswirkung der Schicht den Anforderungen einer dielektrisch behinderten Entladung genügt.In addition to the pellets or alternatively the dielectric on the electrode surfaces with a catalytic active layer made of finely divided carrier materials and catalytically active components. Your Composition can be the one just described Composition to match the ceramic pellets. In In certain applications, the dielectric can be applied to the Electrode surfaces themselves as a catalytically active layer made of finely divided carrier materials and catalytically active Components be formed. The prerequisite for this is that the insulation effect of the layer meets the requirements a dielectric barrier discharge is sufficient.
Die Elektroden des Plasmareaktors können als parallel zueinander ausgerichtete flächige Gebilde aufgebaut sein oder von zwei konzentrisch zueinander angeordneten Rohrelektroden gebildet werden, wobei die elektrische Entladung jeweils im Zwischenraum zwischen den beiden Elektroden abläuft. Im Falle des Reaktors aus zwei parallelen Platten-Elektroden ist wenigstens eine der Elektroden auf den einander gegenüberliegenden Flächen mit einem Dielektrikum beschichtet. Im Falle der konzentrisch angeordneten Rohrelektroden ist wenigstens eine der Elektroden auf den einander gegenüberliegenden Mantelfächen mit einem Dielektrikum beschichtet.The electrodes of the plasma reactor can be considered parallel to each other aligned flat structures can be built up or of two concentrically arranged Tube electrodes are formed, the electrical Discharge in the space between the two Electrodes expires. In the case of the reactor from two parallel plate electrodes is at least one of the Electrodes on the opposite surfaces with coated with a dielectric. In the case of concentric arranged tubular electrodes is at least one of the Electrodes on the opposing jacket surfaces coated with a dielectric.
Zur Erleichterung der Ausbildung von Entladungsfäden können räumliche Inhomogenitäten durch Verwendung dreidimenional strukturierter Elektrodenflächen vorgesehen sein, die zu lokalen Feldüberhöhungen und damit zur Ausbildung der Entladung führen. Wie aus der Literatur bekannt ist, ist die eingekoppelte Elektronenenergie bei einer Plasmaentladung abhängig vom Produkt aus Elektrodenabstand d und Druck p (d*p), so daß bei konstantem Gasdruck allein über die Änderung der Geometrie des Reaktors, bestimmte Radikalreaktionen im Plasma gefördert beziehungsweise unterdrückt werden können. Für das vorgeschlagene Verfahren sollte das Produkt aus Elektrodenabstand und Druck im Bereich zwischen 0,05 und 100 mm*bar liegen.To facilitate the formation of discharge threads spatial inhomogeneities due to the use of three dimensions Structured electrode surfaces can be provided that local field surges and thus for the training of Discharge. As is known from the literature the injected electron energy during a plasma discharge depending on the product from the electrode distance d and pressure p (d * p), so that at constant gas pressure alone about changing the geometry of the reactor Radical reactions promoted in plasma respectively can be suppressed. For the proposed procedure should the product of electrode distance and pressure in the Range between 0.05 and 100 mm * bar.
Die Entladung kann über verschiedenartige Wechselspannungen angeregt werden. Für eine hohe Elektronendichte und möglichst gleichzeitige Ausbildung der Entladung im gesamten Entladungsraum des Reaktors sind pulsförmige Anregungsspannungen mit einer Frequenz zwischen 50 Hz und 250 kHz besonders geeignet. The discharge can take place via various types of alternating voltages be stimulated. For a high electron density and if possible simultaneous formation of the discharge throughout Discharge space of the reactor are pulsed excitation voltages with a frequency between 50 Hz and 250 kHz particularly suitable.
Der Reaktor kann aus jedem elektrisch und thermisch geeigneten Material hergestellt werden. Insbesondere sind Kunststoffe, Keramiken und Gläser zu nennen. Ebenso sind hybride Konstruktionen aus verschiedenen Materialien möglich.The reactor can be any electrically and thermally suitable Material are made. In particular, plastics are To name ceramics and glasses. Are also hybrid Constructions made of different materials possible.
Nach dem Durchlaufen des Plasmareaktors wird der Gasstrom dem mageren Abgas der Verbrennungskraftmaschine zugemischt und über den Katalysator für die selektive katalytische Reduktion geleitet.After passing through the plasma reactor, the gas flow admixed with the lean exhaust gas of the internal combustion engine and about the catalyst for the selective catalytic Reduction led.
Als Katalysator für die selektive katalytische Reaktion
können alle aus dem Stand der Technik bekannten SCR-Katalysatoren
verwendet werden. Beispielhaft seien hier die in
den US-Patenten US 4,916,107, US 5,116,586 und US 5,300,472
beschriebenen Katalysatoren genannt. Die US 4,916,107 und
die US 5,300,472 beschreiben Katalysatoren auf der Basis
von Titanoxid. Im einzelnen enthalten diese Katalysatoren:
Die US 5,116,586 offenbart einen SCR-Katalysator auf der Basis von Zeolithen, der auf einem Zeolith vom Mordenit-Typ Kupfer, Eisen, Molybdän, Cer oder Mischungen davon enthält.US 5,116,586 discloses an SCR catalyst on the Base of zeolite based on a zeolite of the mordenite type Contains copper, iron, molybdenum, cerium or mixtures thereof.
Darüber hinaus sind auch SCR-Katalysatoren bekannt, die als katalytisch aktive Komponente wenigstens ein Platingruppenmetall in hochdisperser Form auf einem geeigneten Trägermaterial enthalten. Als Trägermaterialien können Magnesiumoxid, Aluminiumoxide, Siliziumoxid, Titanoxid, Zirkonoxid und deren Mischungen eingesetzt werden.In addition, SCR catalysts are also known which catalytically active component at least one platinum group metal in highly disperse form on a suitable carrier material contain. Magnesium oxide, Aluminum oxides, silicon oxide, titanium oxide, zirconium oxide and their mixtures are used.
Die genannten Katalysatoren können in Form von Pellets vorliegen oder zu monolithischen Strukturen, insbesondere Wabenkörpern, extrudiert sein. Ebenfalls einsetzbar sind sogenannte Beschichtungskatalysatoren, bei denen der Katalysator in Form einer Schicht auf einem inerten Tragkörper aufgebracht ist.The catalysts mentioned can be in the form of pellets present or to monolithic structures, in particular Honeycomb bodies, extruded. Can also be used So-called coating catalysts, in which the catalyst in the form of a layer on an inert support body is applied.
Das vorgeschlagene Verfahren soll die Stickoxide in sauerstoffreichen, das heißt in mageren Abgasen durch selektive katalytische Reduktion mittels Ammoniak vermindern. Zur Erzeugung des Ammoniaks wird erfindungsgemäß ein fetter, sauerstoffarmer Gasstrom zum Beispiel in Form eines Abgas-Teilstromes benötigt.The proposed method is intended to reduce the nitrogen oxides in oxygen-rich that is, in lean exhaust gases by selective Reduce catalytic reduction with ammonia. For generation According to the invention, the ammonia becomes a fat, low-oxygen Gas flow, for example in the form of a partial exhaust gas flow needed.
In den Figuren 5 und 6 sind beispielhaft zwei verschiedene Möglichkeiten zur Durchführung des Verfahrens an einem Kraftfahrzeug dargestellt.In Figures 5 and 6 are two different examples Ways to perform the procedure on one Motor vehicle shown.
Figur 5 zeigt eine Brennkraftmaschine (10) mit 4 Zylindern (11). Die Maschine wird mit einem mageren Luft/Kraftstoff-Gemisch betrieben, das heißt die Luftzahl λ ist größer als 1 (λ > 1). Da durch die Verbrennung in der Maschine die Luftzahl nicht verändert wird, weist auch das Abgas der Maschine eine Luftzahl von über 1 auf.FIG. 5 shows an internal combustion engine (10) with 4 cylinders (11). The engine runs on a lean air / fuel mixture operated, that is, the air ratio λ is greater than 1 (λ> 1). Because of the combustion in the machine Air ratio is not changed, also shows the exhaust gas Machine has an air ratio of over 1.
Das magere Abgas der vier Zylinder wird in der Abgasleitung (12) zusammengefaßt und erst über einen Katalysator für die selektive Reduktion (13) und dann über einen Oxidationskatalysator (14) geleitet. Der Oxidationskatalysator (14) ist optional. Er soll im Falle einer möglichen Überdosierung von Ammoniak diesen oxidieren und somit eine Emission von Ammoniak verhindern.The lean exhaust gas from the four cylinders is in the exhaust pipe (12) summarized and only over a catalyst for the selective reduction (13) and then over an oxidation catalyst (14) headed. The oxidation catalyst (14) is optional. It should be used in the event of a possible overdose of ammonia oxidize it and thus an emission of Prevent ammonia.
Zur Erzeugung eines fetten Abgas-Teilstromes ist in Figur 5 ein zusätzlicher Brenner (15) vorgesehen, der mit einem unterstöchiometrischen Luft/Kraftstoff-Gemisch (λ < 1) betrieben wird. Vorteilhafterweise kann hierfür eine im Fahrzeug vorhandene Standheizung verwendet werden. Eine solche Standheizung ist häufig bei den hier betrachteten kraftstoffsparenden Fahrzeugen notwendig, um die Fahrgastzelle zu beheizen. Das Abgas des Brenners wird zur Bildung von Ammoniak durch die elektrische Gasentladung eines Plasmareaktors (16) hindurchgeführt und dann vor dem Katalysator für die selektive katalytische Reduktion dem Abgas der Brennkraftmaschine beigemischt. Bezugsziffer (17) bazeichnet die Elektroden des Plasmareaktors.To generate a rich partial exhaust gas flow, FIG an additional burner (15) is provided with a sub-stoichiometric air / fuel mixture (λ <1) operated becomes. This can advantageously be done in the vehicle existing parking heater can be used. Such Auxiliary heating is often used in the fuel-saving models considered here Vehicles necessary to the passenger compartment to heat. The exhaust gas from the burner is used to form Ammonia from the electrical gas discharge of a plasma reactor (16) passed and then in front of the catalyst for the selective catalytic reduction of the exhaust gas Internal combustion engine added. Reference numeral (17) shows ba the electrodes of the plasma reactor.
Die Standheizung erfüllt also einerseits den Zweck der Zusatzbeheizung der Fahrgastzelle, andererseits stellt sie eine einfach steuerbare Komponente zur Erzeugung eines fetten Abgas-Teilstromes dar. Zur Verbesserung der Ammoniak-Ausbeute kann zwischen Brenner und elektrischer Gasentladung ein Wärmetauscher eingebaut werden, der das Abgas abkühlt. Somit wird der Heizungswirkungsgrad nur aufgrund der leicht fetten Betriebsweise, nicht aber durch eine Wärmeenergieentnahme, vermindert.On the one hand, the auxiliary heater fulfills the purpose of additional heating the passenger compartment, on the other hand it provides an easily controllable component for generating a fat Exhaust gas partial flow. To improve the ammonia yield can between burner and electric gas discharge a heat exchanger can be installed to cool the exhaust gas. Thus, the heating efficiency is only due to the slightly greasy mode of operation, but not through heat energy extraction, reduced.
Figur 6 zeigt eine weitere Möglichkeit zur Erzeugung eines fetten Abgas-Teilstromes. (10) bezeichnet hier ebenfalls die Brennkraftmaschine mit vier Zylindern (11) und (11'). In diesem Fall handelt es sich um einen direkteinspritzenden Benzin- oder Dieselmotor mit steuerbarer Einspritzung für jeden Zylinder. Die Zylinder (11) werden mit einem mageren Luft/Kraftstoff-Gemisch (λ > 1) und Zylinder (11') mit einem fetten Luft/Kraftstoff-Gemisch (λ < 1) betrieben. In der Abgasleitung dieses Zylinders (11') befindet sich der Plasmareaktor (16) zur Erzeugung von Ammoniak.Figure 6 shows another way of generating a rich exhaust gas partial flow. (10) also denotes here the internal combustion engine with four cylinders (11) and (11 '). In this case it is a direct injection Gasoline or diesel engine with controllable injection for each cylinder. The cylinders (11) are with a lean air / fuel mixture (λ> 1) and cylinder (11 ') operated with a rich air / fuel mixture (λ <1). In the exhaust pipe of this cylinder (11 ') is the plasma reactor (16) for generating ammonia.
Die beiden Verfahrensschritte (Erzeugung eines fetten Gasstromes und die Ammoniakbildung) können auch zusammengefaßt sein. Dies kann zum Beispiel durch Einspritzen von Kraftstoff zusammen mit einer unterstöchiometrischen Menge Luft in den Plasmareaktor geschehen.The two process steps (generation of a rich gas stream and ammonia formation) can also be summarized his. This can be done, for example, by injecting Fuel along with a substoichiometric amount Air happen in the plasma reactor.
Figur 7 zeigt einen koaxialen Plasmareaktor. (20) bezeichnet ein Außenrohr und (21) ein Innenrohr aus Quarzglas. Die Innenfläche des Innenrohres und die Außenfläche des Außenrohres sind mit metallischen Elektroden (23) und (22) belegt. Durch Anlegen einer Spannungsquelle (24) an diese Elektroden kann im ringförmigen Zwischenraum zwischen Innenrohr und Außenrohr eine dielektrische Barrieren-Entladung gezündet werden.Figure 7 shows a coaxial plasma reactor. (20) an outer tube and (21) an inner tube made of quartz glass. The Inner surface of the inner tube and the outer surface of the outer tube are covered with metallic electrodes (23) and (22). By applying a voltage source (24) to this Electrodes can be in the annular space between Inner tube and outer tube a dielectric barrier discharge be ignited.
Figur 8 zeigt den Querschnitt durch einen wabenförmig aufgebauten Reaktor senkrecht zu den Strömungskanälen (33) für das Abgas. Der Wabenkörper besteht abwechselnd aus Lagen von glatten (31) und gewellten (30) Metallfolien, die beidseitig mit einem Dielektrikum (32) beschichtet sind. Die glatten Folien sind über eine gemeinsame elektrische Leitung mit einem Pol der Hochspannungsquelle (34) und die gewellten Folien mit dem zweiten Pol der Spannungsquelle verbunden. Durch Anlegen einer Spannung findet eine elektrische Entladung in jedem Strömungskanal (33) transversal zur Strömung des Abgases statt. Die Beschichtung der Metallfolien mit dem Dielektrikum isoliert die benachbarten Folien elektrisch gegeneinander. Es können entweder die glatten oder gewellten oder beide Folientypen mit einem Dielektrikum zur gegenseitigen elektrischen Isolation beschichtet sein. Anstelle der dielektrischen Beschichtung besteht die Möglichkeit, eine dielektrische Zwischenschicht zwischen benachbarten Folien einzubringen. Bei dieser Zwischenschicht kann es sich zum Beispiel um eine keramische Folie handeln.FIG. 8 shows the cross section through a honeycomb structure Reactor perpendicular to the flow channels (33) for the exhaust gas. The honeycomb alternately consists of layers of smooth (31) and corrugated (30) metal foils that are coated on both sides with a dielectric (32). The smooth sheets are common across an electrical Line with one pole of the high voltage source (34) and the corrugated foils with the second pole of the voltage source connected. Applying a voltage finds an electrical one Discharge transversely in each flow channel (33) to the flow of the exhaust gas instead. The coating of the Metal foils with the dielectric isolate the neighboring ones Foils electrically against each other. It can be either smooth or corrugated or both types of film with one Dielectric for mutual electrical insulation be coated. Instead of the dielectric coating there is the possibility of a dielectric interlayer between adjacent foils. With this intermediate layer for example, it can be a ceramic one Trade slide.
Wegen der geringen Querschnittsabmessungen der Strömungskanäle kann die Entladungsspannung entsprechend niedrig gewählt werden. Die Länge der Wabenkörper ist nicht beschränkt. In Figur 8 sind gewellte und glatte Metallfolien miteinander kombiniert und bilden einen Folienstapel. Es können jedoch auch zwei verschiedenartig gewellte Metallfolien miteinander kombiniert werden. Die Art der Wellung, ebenso wie die Querschnittsabmessungen der Strömungskanäle können den Anwendungserfordernissen angepaßt werden.Because of the small cross-sectional dimensions of the flow channels the discharge voltage can be correspondingly low to get voted. The length of the honeycomb body is not limited. In Figure 8 there are corrugated and smooth metal foils combined with each other and form a stack of films. It can also use two differently corrugated metal foils can be combined with each other. The type of curl, as well as the cross-sectional dimensions of the flow channels can be adapted to the application requirements.
Auch bei diesem Reaktor kann auf die dielektrischen Schichten, welche die Metallfolien gegen die Gasentladung und untereinander isolieren, eine Katalysatorschicht aus feinteiligen Trägermaterialien und katalytisch aktiven Komponenten aufgebracht werden. Alternativ hierzu können die dielektrischen Schichten selbst als katalytisch aktive Schicht aus feinteiligen Trägermaterialien und katalytisch aktiven Komponenten ausgebildet sein, wenn diese Schicht eine den Anforderungen der dielektrisch behinderten Entladung genügende Isolationswirkung aufbringt. Die Zusammensetzung dieser katalytisch aktiven Schicht kann der schon für die keramischen Pellets beschriebenen Zusammensetzung entsprechen.In this reactor too, the dielectric layers, which the metal foils against the gas discharge and each other isolate a catalyst layer made of fine particles Carrier materials and catalytically active components be applied. Alternatively, the dielectric layers themselves as catalytically active Layer of finely divided carrier materials and catalytic active components if this layer a the requirements of dielectric barrier discharge has sufficient insulation effect. The composition this catalytically active layer can for the composition described for the ceramic pellets correspond.
Das vorgeschlagene Verfahren besitzt gegenüber den bekannten Verfahren verschiedene Vorteile. Es ist zum Beispiel auf verschiedene Motorkonzepte anwendbar. Beim Einsatz an Magermotoren verschlechtern sich die Verbrauchswerte für den Kraftstoff nur geringfügig. Besonders vorteilhaft ist die Erzeugung von Ammoniak an Bord des Kraftfahrzeugs, ohne die Notwendigkeit zusätzliche Betriebsstoffe mitführen zu müssen. Die notwendige Menge an Ammoniak kann über die elektrischen und geometrischen Parameter der Gasentladung sowie über die Bereitstellung des fetten Abgas-Teilstromes eingestellt werden. Die Steuerung dieses Vorganges kann dabei von der Motorelektronik vorgenommen werden.The proposed method has compared to the known Procedure various advantages. For example it is applicable to different engine concepts. When using Lean engines worsen consumption values for the fuel only slightly. It is particularly advantageous the generation of ammonia on board the motor vehicle without the need to carry additional supplies have to. The necessary amount of ammonia can be over electrical and geometric parameters of gas discharge as well as the provision of the rich exhaust gas partial flow can be set. The control of this process can be carried out by the engine electronics.
Für die folgenden Untersuchungen zur Bildung von Ammoniak
durch Behandeln eines fetten Gasstromes in einer
Plasmaentladung wurde der koaxiale Reaktor von Figur 7 eingesetzt.
Außen- und Innenrohr bestanden aus 2 mm dickem
Quarzglas. Das Außenrohr hatte einen Außendurchmesser von 4
und das Innenrohr einen Innendurchmesser von 2,6 cm. Die
Länge des Reaktors betrug 20 und die Länge der Elektroden
16 cm. Der Gasentladungsraum zwischen den beiden Quarzrohren
war mit einem Palladium-Pelletkatalysator (3,2 g
Palladium und 35 g Bariumoxid auf einem Liter Pellets aus
γ-Aluminiumoxid) gefüllt. For the following studies on the formation of ammonia
by treating a rich gas stream in one
The coaxial reactor of FIG. 7 was used for plasma discharge.
The outer and inner tubes consisted of 2 mm thick
Quartz glass. The outer tube had an outer diameter of 4
and the inner tube has an inner diameter of 2.6 cm. The
Length of the reactor was 20 and the length of the
Durch den Reaktor wurde die in der Tabelle 1 angegebene Synthesegasmischung mit einem Volumenstrom von 4,5 Nl/min bei Atmosphärendruck und einer Temperatur von 100°C geführt. Das Produkt d*p betrug 6 mm*bar. Durch Anlegen einer Wechselspannung mit einer Frequenz von 1 kHz und einer Amplitude von etwa 11 kV wurde im Reaktor eine Barrieren-Entladung gezündet.Through the reactor, the one given in Table 1 was obtained Synthesis gas mixture with a volume flow of 4.5 Nl / min performed at atmospheric pressure and a temperature of 100 ° C. The product d * p was 6 mm * bar. By creating one AC voltage with a frequency of 1 kHz and one An amplitude of about 11 kV was a barrier discharge in the reactor ignited.
Die Messungen wurden bei Raumtemperatur durchgeführt.
Die Synthesegasmischung von Tabelle 1 ist mager, das heißt sie weist einen überstöchiometrischen Sauerstoffgehalt auf (Die Luftzahl λ ist größer als 1.). Unter diesen Bedingungen wird beim Einschalten der Gasentladung Stickstoffmonoxid vom Pellet-Katalysator adsorbiert. Dies kann durch die Umsetzung von NO zu NO2 im Plasmareaktor bei Luftüberschuß und nachfolgender weiterer Oxidation und Speicherung als NO3 - erklärt werden. Wird von der mageren Abgaszusammensetzung auf eine fette Zusammensetzung umgeschaltet, so findet eine Desorption des zuvor adsorbierten Stickstoffmonoxids statt. Gleichzeitig bildet sich in der Gasentladung Ammoniak, welches das desorbierte Stickoxid sehr effektiv zu Stickstoff und Wasser umsetzt. The synthesis gas mixture in Table 1 is lean, which means that it has an over-stoichiometric oxygen content (the air ratio λ is greater than 1.). Under these conditions, nitrogen monoxide is adsorbed by the pellet catalyst when the gas discharge is switched on. Be explained - may be caused by the conversion of NO to NO 2 in the plasma reactor at excess air and subsequent further oxidation and storage as NO. 3 If a switch is made from the lean exhaust gas composition to a rich composition, the previously adsorbed nitrogen monoxide is desorbed. At the same time, ammonia is formed in the gas discharge, which very effectively converts the desorbed nitrogen oxide into nitrogen and water.
Im vorliegenden Beispiel wurde die Umschaltung von magerem auf fettes Abgas durch Abschalten der Sauerstoffzufuhr und Zuschalten von Kohlenmonoxid vorgenommen.In the present example, switching from lean to rich exhaust gas by switching off the oxygen supply and Activation of carbon monoxide made.
Figur 9 bis 12 belegen die oben beschriebenen Vorgänge. Figur 9 zeigt den Verlauf der Konzentration von Stickstoffmonoxid im Synthesegas hinter dem Plasmareaktor in Abhängigkeit von der in die Gasentladung eingekoppelten elektrischen Leistung. Bei ausgeschalteter Gasentladung (elektrische Leistung 0) wird hinter dem Plasmareaktor die NO-Konzentration der Synthesegasmischung von 500 ppm gemäß Tabelle 1 gemessen. Nach Einschalten der Gasentladung findet sofort eine starke Verminderung der NO-Konzentration statt. Dies ist auf die Bildung von Stickstoffdioxid durch die Plasmaentladung zurückzuführen, welches sehr effektiv von den Katalysatorpellets adsorbiert wird.Figures 9 to 12 demonstrate the processes described above. FIG. 9 shows the course of the concentration of nitrogen monoxide depending on the synthesis gas behind the plasma reactor of the electrical coupled into the gas discharge Power. When the gas discharge is switched off (electrical Performance 0) is the NO concentration behind the plasma reactor according to the synthesis gas mixture of 500 ppm Table 1 measured. After switching on the gas discharge immediately finds a sharp reduction in the NO concentration instead of. This is due to the formation of nitrogen dioxide attributed to the plasma discharge, which is very effective is adsorbed by the catalyst pellets.
Die elektrische Leistung der Plasmaentladung wurde langsam erhöht. Bei einer Leistung von etwa 9 Watt wurde die Zusammensetzung der Synthesegasmischung von mager auf fett durch Abschalten von Sauerstoff und Zuführen von Kohlenmonoxid geändert. Figur 9 zeigt nach dem Umschalten der Abgaszusammensetzung zunächst eine starke Desorption von Stickstoffmonoxid unter den jetzt vorliegenden reduzierenden Abgasbedingungen. Gleichzeitig wird durch die Plasmaentladung Ammoniak unter Verbrauch von Stickstoffmonoxid und gegebenenfalls weiterer stickstoffhaltiger Verbindungen des Gasstromes (z.B. N2) gebildet.The electrical output of the plasma discharge was slowly increased. At an output of approximately 9 watts, the composition of the synthesis gas mixture was changed from lean to rich by switching off oxygen and adding carbon monoxide. FIG. 9 shows after the switching of the exhaust gas composition a strong desorption of nitrogen monoxide under the reducing exhaust gas conditions now present. At the same time, ammonia is formed by the plasma discharge using nitrogen monoxide and possibly further nitrogen-containing compounds of the gas stream (for example N 2 ).
Figuren 10 bis 12 zeigen spektroskopische Untersuchungen des Abgases während der mageren Betriebsphase, während des Umschaltens von mager auf fette Betriebsweise und während der fetten Betriebsphase. Während der mageren Phase zeigt das Abgas nur die Absorptionsbanden von Stickstoffmonoxid. Während der Umschaltphase verschwinden diese Absorptionsbanden (Figur 11) und während der fetten Betriebsphase zeigt das Abgas deutlich die Absorptionsbanden des gebildeten Ammoniaks (Figur 12). Figures 10 to 12 show spectroscopic examinations of the exhaust gas during the lean operating phase, during the Switching from lean to rich mode and during the fat operating phase. Shows during the lean phase the exhaust gas only the absorption bands of nitrogen monoxide. These absorption bands disappear during the switching phase (Figure 11) and during the rich operating phase the exhaust gas clearly shows the absorption bands of the formed Ammoniaks (Figure 12).
Dieser Versuch wurde mit den folgenden Zusammensetzungen
der Pellets im Plasmareaktor wiederholt:
In allen Fällen zeigte sich eine deutliche Bildung von Ammoniak in der Gasentladung unter reduzierenden Abgasbedingungen.In all cases there was a clear formation of Ammonia in the gas discharge under reducing exhaust gas conditions.
Claims (28)
dadurch gekennzeichnet,
daß der fette Gasstrom durch einen unterstöchiometrisch betriebenen Brenner erzeugt wird.Method according to claim 1,
characterized,
that the rich gas stream is generated by a substoichiometrically operated burner.
dadurch gekennzeichnet,
daß der fette Gasstrom einen Teil des Abgasstromes der Verbrennungskraftmaschine bildet und durch Betreiben eines Zylinders der Maschine mit einem unterstöchiometrischen Luft/Kraftstoff-Gemisch gewonnen wird.Method according to claim 1,
characterized,
that the rich gas flow forms part of the exhaust gas flow of the internal combustion engine and is obtained by operating a cylinder of the machine with a substoichiometric air / fuel mixture.
dadurch gekennzeichnet,
daß der fette Gasstrom durch Einspritzen von Kohlenwasserstoffen in einen Luftstrom gebildet wird. Method according to claim 1,
characterized,
that the rich gas stream is formed by injecting hydrocarbons into an air stream.
dadurch gekennzeichnet,
daß der fette Gasstrom zur Bildung des für die Reduktion benötigten Ammoniaks in einem elektrischen Gasentladungsplasma behandelt wird.Method according to claim 1,
characterized,
that the rich gas stream to form the ammonia required for the reduction is treated in an electrical gas discharge plasma.
dadurch gekennzeichnet,
daß als Gasentladung eine dielektrisch behinderte Entladung bei Atmosphärendruck mit einem Produkt (d*p) aus Elektrodenabstand und Druck zwischen 0,05 und 100 mm*bar eingesetzt wird.Method according to claim 5,
characterized,
that a dielectric barrier discharge at atmospheric pressure with a product (d * p) of electrode spacing and pressure between 0.05 and 100 mm * bar is used as the gas discharge.
dadurch gekennzeichnet,
daß die Entladung in den Strömungskanälen eines Wabenkörpers angeregt wird, welcher durch Übereinanderstapeln von abwechselnd glatten und gewellten Metallfolien erhalten wurde, wobei entweder die glatten oder gewellten oder beide Folientypen mit einem Dielektrikum zur gegenseitigen elektrischen Isolation beschichtet sind und die Entladungsspannung zwischen allen glatten und allen gewellten Folien angelegt wird.Method according to claim 6,
characterized,
that the discharge is excited in the flow channels of a honeycomb body, which was obtained by stacking alternately smooth and corrugated metal foils, either the smooth or corrugated or both types of film are coated with a dielectric for mutual electrical insulation and the discharge voltage between all smooth and all corrugated Foils is created.
dadurch gekennzeichnet,
daß auf die Beschichtung der Metallfolien mit dem Dielektrikum eine Katalysatorschicht aus feinteiligen Trägermaterialien und katalytisch aktiven Komponenten aufgebracht ist.Method according to claim 7,
characterized,
that a catalyst layer composed of finely divided support materials and catalytically active components is applied to the coating of the metal foils with the dielectric.
dadurch gekennzeichnet,
daß das Dielektrikum durch eine Katalysatorbeschichtung aus feinteiligen Trägermaterialien und katalytisch aktiven Komponenten gebildet wird. Method according to claim 7,
characterized,
that the dielectric is formed by a catalyst coating made of finely divided support materials and catalytically active components.
dadurch gekennzeichnet,
daß als feinteilige Trägermaterialien Aluminiumoxid, Titanoxid, Zirkonoxid, Ceroxid, Siliciumdioxid, Magnesiumoxid oder deren Mischoxide und Zeolithe verwendet werden.Method according to claim 8 or 9,
characterized,
that aluminum oxide, titanium oxide, zirconium oxide, cerium oxide, silicon dioxide, magnesium oxide or their mixed oxides and zeolites are used as finely divided carrier materials.
dadurch gekennzeichnet,
daß die feinteiligen Trägermaterialien mit Siliciumdioxid und/oder Seltenerdoxiden stabilisiert sind.A method according to claim 10,
characterized,
that the finely divided carrier materials are stabilized with silicon dioxide and / or rare earth oxides.
dadurch gekennzeichnet,
daß die Katalysatorbeschichtung mindestens eine der katalytisch aktiven Komponenten Platin, Palladium, Rhodium und Iridium in hochdisperser Form enthält.A method according to claim 10,
characterized,
that the catalyst coating contains at least one of the catalytically active components platinum, palladium, rhodium and iridium in highly dispersed form.
dadurch gekennzeichnet,
daß die Katalysatorbeschichtung zusätzlich mindestens ein basisches Oxid der Alkali- oder Erdalkalimetalle des Periodensystems der Elemente enthält.A method according to claim 10,
characterized,
that the catalyst coating additionally contains at least one basic oxide of the alkali or alkaline earth metals of the periodic table of the elements.
dadurch gekennzeichnet,
daß die Entladung zwischen zwei parallelen Elektroden erzeugt wird, von denen wenigstens eine auf den einander gegenüberliegenden Flächen mit einem Dielektrikum beschichtet ist.Method according to claim 6,
characterized,
that the discharge is generated between two parallel electrodes, at least one of which is coated on the opposite surfaces with a dielectric.
dadurch gekennzeichnet,
daß die Entladung im Ringraum zwischen zwei konzentrisch zueinander angeordneten Rohrelektroden erzeugt wird, von denen wenigstens eine auf den einander gegenüberliegenden Mantelflächen der rohrförmigen Elektroden mit einem Dielektrikum beschichtet ist. Method according to claim 6,
characterized,
that the discharge is generated in the annular space between two tube electrodes arranged concentrically to one another, at least one of which is coated with a dielectric on the mutually opposite lateral surfaces of the tubular electrodes.
dadurch gekennzeichnet,
daß der Entladungsraum zwischen den Elektroden mit keramischen Pellets gefüllt ist.A method according to claim 14 or 15,
characterized,
that the discharge space between the electrodes is filled with ceramic pellets.
dadurch gekennzeichnet,
daß die keramischen Pellets aus mindestens einem feinteiligen Trägermaterial ausgewählt aus der Gruppe Aluminiumoxid, Titanoxid, Zirkonoxid, Ceroxid, Siliciumdioxid, Magnesiumoxid oder deren Mischoxide und Zeolithen bestehen.A method according to claim 16,
characterized,
that the ceramic pellets consist of at least one finely divided carrier material selected from the group aluminum oxide, titanium oxide, zirconium oxide, cerium oxide, silicon dioxide, magnesium oxide or their mixed oxides and zeolites.
dadurch gekennzeichnet,
daß die feinteiligen Trägermaterialien mit Siliciumdioxid und/oder Seltenerdoxiden stabilisiert sind.A method according to claim 17,
characterized,
that the finely divided carrier materials are stabilized with silicon dioxide and / or rare earth oxides.
dadurch gekennzeichnet,
daß die keramischen Pellets mindestens eine der katalytisch aktiven Komponenten Platin, Palladium, Rhodium und Iridium in hochdisperser Form enthalten.A method according to claim 17,
characterized,
that the ceramic pellets contain at least one of the catalytically active components platinum, palladium, rhodium and iridium in highly dispersed form.
dadurch gekennzeichnet,
daß die keramischen Pellets zusätzlich mindestens ein basisches Oxid der Alkali- oder Erdalkalimetalle des Periodensystems der Elemente enthalten.A method according to claim 17,
characterized,
that the ceramic pellets additionally contain at least one basic oxide of the alkali or alkaline earth metals of the periodic table of the elements.
dadurch gekennzeichnet,
daß auf das Dielektrikum eine Katalysatorschicht aus feinteiligen Trägermaterialien und katalytisch aktiven Komponenten aufgebracht ist.A method according to claim 14 or 15,
characterized,
that a catalyst layer of finely divided support materials and catalytically active components is applied to the dielectric.
dadurch gekennzeichnet,
daß das Dielektrikum durch eine Katalysatorbeschichtung aus feinteiligen Trägermaterialien und katalytisch aktiven Komponenten gebildet wird.A method according to claim 14 or 15,
characterized,
that the dielectric is formed by a catalyst coating made of finely divided support materials and catalytically active components.
dadurch gekennzeichnet,
daß die Entladung mit einer gepulsten Spannung mit einer Frequenz zwischen 50 Hz und 250 kHz angeregt wird.Method according to one of claims 7 to 9 and 14 or 15,
characterized,
that the discharge is excited with a pulsed voltage with a frequency between 50 Hz and 250 kHz.
dadurch gekennzeichnet,
daß die Entladung mit einer Wechselspannung zwischen 0,2 und 15 kV und einer Frequenz zwischen 50 Hz und 250 kHz angeregt wird.Method according to one of claims 7 to 9 and 14 or 15,
characterized,
that the discharge is excited with an alternating voltage between 0.2 and 15 kV and a frequency between 50 Hz and 250 kHz.
dadurch gekennzeichnet,
daß die Wechselspannung mit einer Frequenz zwischen 0,01 und 10 Hz getaktet betrieben wird.A method according to claim 24,
characterized,
that the AC voltage is operated clocked at a frequency between 0.01 and 10 Hz.
dadurch gekennzeichnet,
daß die Elektrodenflächen dreidimensional strukturiert sind.Method according to one of claims 7 to 9 and 14 or 15,
characterized,
that the electrode surfaces are structured three-dimensionally.
dadurch gekennzeichnet,
daß für die selektive katalytische Reduktion ein Reduktions-Katalysator verwendet wird, der die folgenden Komponenten enthält:
characterized,
that a reduction catalyst is used for the selective catalytic reduction, which contains the following components:
dadurch gekennzeichnet,
daß für die selektive katalytische Reduktion ein Zeolith-Katalysator verwendet wird, der auf einem Zeolith vom Mordenit-Typ Kupfer, Eisen, Cer oder Mischungen davon enthält.Method according to claim 1,
characterized,
that a zeolite catalyst is used for the selective catalytic reduction, which contains copper, iron, cerium or mixtures thereof on a zeolite of the mordenite type.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE19903533A DE19903533A1 (en) | 1999-01-29 | 1999-01-29 | Process for the selective catalytic reduction of nitrogen oxides in oxygen-containing exhaust gases |
DE19903533 | 1999-01-29 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1023935A1 true EP1023935A1 (en) | 2000-08-02 |
EP1023935B1 EP1023935B1 (en) | 2004-06-30 |
Family
ID=7895781
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Application Number | Title | Priority Date | Filing Date |
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EP00101564A Expired - Lifetime EP1023935B1 (en) | 1999-01-29 | 2000-01-27 | Process for selective catalytic reduction of nitrogen oxides in oxygen-containing exhaust gases |
Country Status (4)
Country | Link |
---|---|
US (1) | US6334986B2 (en) |
EP (1) | EP1023935B1 (en) |
JP (1) | JP2000271447A (en) |
DE (2) | DE19903533A1 (en) |
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EP1908932A2 (en) * | 2006-09-26 | 2008-04-09 | Faurecia Abgastechnik GmbH | Exhaust gas facility for diesel vehicles with an SCR catalytic converter |
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CN102084097B (en) * | 2008-05-02 | 2013-11-20 | 通用汽车环球科技运作公司 | Passive ammonia-selective catalytic reduction for NOx control in internal combustion engines |
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DE102010033787B4 (en) * | 2010-08-09 | 2012-04-19 | PLASUS Ingenieurbüro Dr. Thomas Schütte | A method of determining an oxygen concentration in an atmospheric pressure plasma chamber during a plasma process |
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WO2022029079A1 (en) * | 2020-08-04 | 2022-02-10 | Cinogy Gmbh | Gas purification device and method for purifying a gas |
Also Published As
Publication number | Publication date |
---|---|
EP1023935B1 (en) | 2004-06-30 |
DE19903533A1 (en) | 2000-08-10 |
DE50006915D1 (en) | 2004-08-05 |
JP2000271447A (en) | 2000-10-03 |
US20010002244A1 (en) | 2001-05-31 |
US6334986B2 (en) | 2002-01-01 |
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